Opponents of a nationwide child allowance have launched their campaign ahead of a November vote, saying it is unnecessary and will cost too much.
It comes after the government and supporters of a unified benefit put their case, arguing that the economy can stand the extra costs, and that families' purchasing power will increase.
At present the country's 26 cantons set their own child benefit levels, which vary widely. The government says it is now time to do away with the regional discrepancies.
The "no" committee began its campaign in Bern on Wednesday, saying that Switzerland could simply not afford a new allowance.
Pierre Triponez, a centre-right Radical parliamentarian and director of the Association of Small and Medium-sized Businesses that backed the referendum against parliament's decision, called the planned allowance "a big mistake".
"Before we introduce new benefits, we need to review the current social security system and ensure its long-term survival," he said.
Françoise Saudan, a Radical senator, said that a unified benefit went against Switzerland's federal traditions, adding that there was no need to meddle with a system that has worked well so far.
"There is no reason for the federal authorities to become involved in something the cantons have dealt with successfully," she warned, pointing out that differences in the amounts paid by the cantons were explained by salary levels and local purchasing power.
For Saudan, the federal authorities should concentrate on making life simpler for families rather than handing out more money.
Opponents fear that small and medium-sized enterprises (SMEs) will suffer if voters accept the law. Parliamentarian Adrian Amstutz of the rightwing Swiss People's Party warned that the extra costs involved would be a burden on these companies.
"The interior minister might think a 0.2-per cent increase in costs is nothing, but for SMEs that aren't rolling in money, it could have a major impact," he added.
Supporters of the single child allowance launched their own campaign on Tuesday, saying that SFr200 ($157) per month and per child would benefit all of society. The centre-left Social Democrats, the Greens, the centre-right Christian Democrats and the unions all reckon that the cost of the reform is not too high.
"The law is a moderate compromise that will represent real progress," said Social Democrat parliamentarian Liliane Maury Pasquier, adding that most families had seen their purchasing power shrink by ten per cent over the past decade.
They reject claims that the economy will suffer. Hugo Fasel, the head of Travail.Suisse, one of the country's biggest unions, said the extra cost would only be SFr340 million, or at most SFr9 per month and per employee.
Voters will have the final say on November 26.
swissinfo with agencies
Parliament approved the payment of a uniform monthly minimum SFr200 child benefit and SFr250 for children above 16.
The Swiss business community and part of the political right have challenged the decision.
The scheme would cost SFr600 million annually - SFr450 million from employers and at least SFr140 million from government resources.
Currently the payment of child benefits differs from canton to canton, ranging from SFr150 to nearly SFr290 per month.